Graphene oxide has recently been considered as a novel material for use in temperature and humidity sensors. The use of graphene oxide as the sensing material enables transparent, flexible sensors to be produced at low cost with improved sensitivity when compared to existing sensors. Such sensors, however, have been found to suffer from the following drawbacks:                (i) Structural degradation—it is known that irreversible modification of graphene oxide occurs during exposure to water (both liquid and vapour) and is thought to be accelerated when there is current flow through the graphene oxide layer.        (ii) Low conductivity—graphene oxide is an insulator and graphene oxide layers of <50 nm in thickness (required for transparency and speed) have sheet resistances of >GΩ/sq. For typical interdigitated electrode designs, especially those using printed electrodes, this constrains the footprint of the sensor to be several tens of mm2. In some circumstances it may be desirable to shrink this sensor layout size.        (iii) AC operation—it has been observed that the operation of graphene oxide sensors under a DC bias results in the build up of an open circuit voltage across the graphene oxide sensing layer and instability in the DC conductance measurement. This has led to the graphene oxide sensors being measured using either AC or pulsed excitation. In some circumstances DC operation may be desirable.        (iv) Sensitivity—although graphene oxide is highly sensitive to relative humidity, a trade-off exists between sensitivity and thickness (which affects transparency and speed).        
One or more aspects/embodiments of the present disclosure may or may not address one or more of these issues.
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